1. Field of the Invention
The present invention relates to a method and device for controlling rotation speed of a spindle of an optical disk drive, and more particularly, to a method for controlling the rotation speed of the spindle of the optical disk drive by using a wobble signal and an encoder EFM frame synchronization (EEFS) signal.
2. Description of the Prior Art
In this modern information-based society, storing large amounts of information is a most important issue. Among the different kinds of storage media, compact disks (CDs) have become one of the most popular means of mass storage by virtue of their thin size and high storage capacity. Increasingly popular are recordable and rewritable CDs, which enable users of PCs having CD-R or CD-RW drives to record data to CDs.
To adequately manage data, the storage region of the CD is fragmented into many small frames. The CD also has a storage format that must be determined before writing data to a CD. An optical disk drive ascertains the storage format of the CD in advance to writing data onto the CD. The storage format refers additional frame information, including minute, second, and frame number that uniquely distinguish each frame. This additional frame information is known as Absolute Time in Pre-groove (ATIP).
Please refer to FIG. 1, which is a top view of a prior art CD 10. It is well known in the art that the CD 10 has a reflective layer 13 that can reflect laser light. When the CD 10 is placed inside a CD-R drive (not shown), an optical pickup head emits laser light that is modulated by different reflection-modes and different parts of the reflective layer 13. The laser light is reflected back to the optical pickup head of the CD-R drive so the CD-R drive can read information stored on the CD 10. Following the curvature of the CD 10, the reflective layer 13 has a thin, long spiral track 11. View 1A shows a magnified region of the track 11. Track 11 comprises a data track 12 for recording information, and a wobble track 14 for recording the frame information of each frame of the CD 10. The data track 12 follows a spiral path along the curvature of the CD 10, but appears as a straight line in the magnified view 1A. When viewed close-up, the wobble track 14 reveals an oscillatory spiral shape that is also shown following a straight path in magnified view 1A. The wobble track 14 is made up of two different intervals D1 and D2, which have different periods.
Magnified view 1B shows further detail of the data track 12 and the wobble track 14. The data track 12 is made up of discontinuous record marks 16 of varying length that store data. Data written to the CD 10 is encoded by controlling the length of the record marks 16. The wobble track 14 is used for storing information of each frame and is a continuous pair of tracks protruding out of the reflective layer 13. The raised structure of the wobble track 14 is shown in FIG. 2, which is a perspective view of magnified region 1B. In FIG. 2 the wobble track 14 is shown protruding out of the reflective layer 13, and the data track 12 comprising the record marks 16 is located in the groove between the protruding wobble tracks 14.
During the production of the CD 10, the wobble track 14 is made in advance to provide an ATIP signal to the CD-R drive so that data can be written to and read from the CD 10. The ATIP is generated from the wobble track 14 by means of frequency modulation (FM).
Please refer to FIG. 3. FIG. 3. is a schematic diagram showing a prior art wobble signal 18 and a prior art ATIP signal 20. Since the wobble track 14 includes regions of two different periods D1 and D2, when the laser light is reflected by the wobble track 14 the generated wobble signal 18 comprises intervals of pulses of two different frequencies T1 and T2. The T1 interval of the wobble signal 18 represents a binary “1”, and the T2 interval a binary “0”. The corresponding ATIP signal 20 is thus generated by FM demodulation of the wobble signal 18. By demodulating the ATIP signal 20 a bi-phase signal 22 is generated, as summarized in the next paragraph.
Please refer to FIG. 4, which is a schematic diagram of a prior art bi-phase signal 22a generation process. When a logic level change of a signal 20a occurs in the middle of a bit cell, a binary “1” is represented in bi-phase signal 22a, as shown in the regions A and A″. Conversely, if a logic level of a bit cell “B” of the signal 20a remains “1”, the bi-phase signal 22a is a binary “0” level. Similarly, if a logic level of a bit cell “C” of the signal 20a remains “0”, the bi-phase signal 22a is also a binary “0”. Accordingly, the interval between two contiguous changes in logic level is 1T or 2T.
Please refer to FIG. 5, which is a schematic diagram of a prior art ATIP 23. The ATIP 23 is composed of several blocks, and each of the blocks is 42 bits in length. The ATIP 23 includes a 4-bit sync mark 24, a 24-bit data code 26, and a 14-bit cyclic redundancy check 28. The 24-bit data code 26 comprises information of minutes 29, seconds 30, and frames 31. After the ATIP 23 has been bi-phased, the 84-bit bi-phase data signal 22 is generated.
Please refer to FIG. 4 and FIG. 6. FIG. 6 is a schematic diagram of the sync mark 24 shown in FIG. 5. As shown in FIG. 4, the legal interval between two changes in level is 1T or 2T. However, there is still an illegal interval, 3T, available to detect the sync mark 24 in the header of the ATIP 23. The ATIP signal 20 format of the sync mark 24 is “3T-1T-1T-3T”. Reading the sync mark 24 referencing an ATIP clock 32 generates a sync detecting signal 34. In this way, the optical disk drive uses the sync mark 24 to acquire information about the position of the CD 10 and establish a reference point so that the optical disk drive can record data onto the CD 10.
Please refer to FIG. 7A, which is a schematic diagram of a prior art frame. Data is stored on the CD 10 in the format of Eight to Fourteen Modulation (EFM) frames. An ATIP frame comprises 98 EFM frames, F1 to F98. Referring to FIG. 7B, each frame is composed of 588 bits, including sync data, subcode data, main data, p-parity, and q-parity. The main data, p-parity and q-parity form a main channel for storing the entity data, and the subcode data form a sub channel for storing information relative to the entity data, such as track number. In addition, as shown in FIG. 7C, the subcode data S0 of the first frame F1 and the subcode data S1 of the second frame F2 in the ATIP frame generate a subcode sync, which can be used to detect the synchronicity of an ATIP signal and a writing signal.
Moreover, the optical disk drive performs EFM to the data about to be stored according to an EFM write clock. The EFM write clock is synchronized with the writing data. The optical disk drive generates two reference clocks according to the EFM write clock. The first is an encoder EFM frame sync (EEFS), and the second is an encoder subcode frame sync (ESFS). Each frame data generates a corresponding EEFS, and each ATIP frame generates a corresponding ESFS. Since 98 frames form an ATIP frame, the frequency of the ESFS is 98 times that of the EEFS. The ESFS can thus serve as a reference signal to be compared with the ATIP in order to detect the synchronicity between the written data and the CD frame.
Please refer to FIG. 8, which is a schematic diagram of prior art ESFS 42 and ATIP sync 40. According to the Orange Book definition, the deviation 35 between the ATIP sync 40 and the ESFS 42 must be controlled to be within two frames. If the deviation 35 is too large, problems such as overlapping arise.
The prior art method for controlling rotation speed of a spindle in art optical disk drive controls the motor using the wobble signal and EEFS of a CD, and causes the track of the CD run at a constant linear velocity. When the optical disk drive has entered the writing made and prepares to write data onto the CD, the optical disk drive controls the motor by the phase difference between the ATIP sync and the ESFS. The optical disk drive further changes the phase difference by passing the signal through a low pass filter (LPF) to adjust the rotation speed of the motor, so as to make the deviation between the ATIP sync and the ESFS meet the standard. However, the prior art only applies an LPF to adjust the rotation speed of the motor in order to change the phase difference between the ATIP sync and the ESFS. When the phase difference becomes too large causing the rotation speed of the motor to be too fast, the LPF needs more response time to control the rotation speed of the motor. In addition, controlling the motor by the phase difference of the ATIP sync and the ESFS results in the drawback of a slow update rate.